This application is generally in the area of biocompatible polymeric materials which can be applied to biological and non-biological surfaces to minimize cell-cell interactions and adhesion of cells or tissue to the surfaces.
There is a need for materials, and methods of use thereof, which can be used to encapsulate cells and tissues or biologically active molecules which are biocompatible, and which do not elicit specific or non-specific immune responses. An important aspect of the use of these materials in vivo is that they must be applied within the time of a short surgical procedure or before the material to be encapsulated disperses, is damaged or dies.
It is often desirable to implant exogenous cells into a patient, for example, to produce various products the patient is incapable of preparing. An example of this is implantation of exogenous Islets of Langerhans cells to produce insulin in a diabetic patient. However, unless protected, exogenous cells are destroyed immediately following transplantation. Numerous attempts have been made to encapsulate the cells to minimize the body""s efforts to destroy them.
Cells have been encapsulated using the ionic crosslinking of alginate (a polyanion) with polylysine or polyornithine (polycation) (Goosen, et al., Biotechnology and Bioengineering, 27:146 (1985)). This technique offers relatively mild encapsulating conditions. Microcapsules formed by the coacervation of alginate and poly(L-lysine) have been shown to be immunoprotective. However, the capsules do not remain intact long after implantation, or are quickly surrounded by fibrous tissue.
The biocompatibility of alginate-poly(L-lysine) microcapsules has been reported to be significantly enhanced by incorporating a graft copolymer of PLL and PEO on the microcapsule surface (Sawhney, et al., Biomaterials, 13, 863-870 (1991)). The PEO chain is highly water soluble and highly flexible. PEO chains have an extremely high mobility in water and are essentially non-ionic in structure. Immobilization of PEO on a surface has been largely carried out by the synthesis of graft copolymers having PEO side chains.
U.S. Pat. Nos. 5,573,934 and 5,626,863 to Hubbell et al. disclose hydrogel materials including a water-soluble region such as polyethylene glycol and a biodegradable region, including various biodegradable polymers such as polylactide and polyglycolide, terminated with photopolymerizable groups such as acrylates. These materials can be applied to a tissue surface and polymerized, for example, to form tissue coatings. These materials are adhered to tissue surfaces by polymerizing the photopolymerizable groups on the materials after they have been applied to the tissue surface.
U.S. Pat. No. 5,627,233 to Hubbell et al. discloses multifunctional polymeric materials for use in inhibiting adhesion and immune recognition between cells and tissues. The materials include a tissue binding component (polycation) and a tissue non-binding component (polynonion). In particular, Hubbell discloses various PEG/PLL copolymers, with molecular weights greater than 300, with structures which include AB copolymers, ABA copolymers, and brush-type copolymers. These polymers are being commercially developed for use as tissue sealants and to prevent surgical adhesions.
It is therefore an object of the present invention to provide a polymeric material that can be applied to living cells and tissues, in a very short time period, to protect the cells and tissues from cell to cell interactions, such as adhesion.
It is a further object of the present invention to provide a polymeric material which is biocompatible and resistant to degradation for a specific time period.
It is a further object of the present invention to provide compositions for inhibiting tissue adhesion and cell-cell contact within the body, as well as methods for making and using the compositions.
Compositions for encapsulating cells and for coating biological and non-biological surfaces, which minimize or prevent cell-cell contact and tissue adhesion, and methods of preparation and use thereof, are disclosed. Embodiments include polyethylene glycol/polylysine (PEG/PLL) block or comb-type copolyrners with high molecular weight PLL (greater than 1000, more preferably greater than 100,000); PEG/PLL copolymers in which the PLL is a dendrimer which is attached to one end of the PEG; and multilayer compositions including alternating layers of polycationic and polyanionic materials. In the PEGIPLL dendrimers, the molecular weight of the Pit is between 1,000 and 1,000,000, preferably greater than 100,000, more preferably, between 300,000 and 800,000, and the molecular weight of the PEG is between 500 and 2,000,000, preferably greater than 50,000. more preferably between 5,000 and 100,000. For PEG of MW 5000, the optimal ratio is between 1 PEG chain for every 3 to 10, preferably 5 to 7, lysine subunits. The optimal ratio for PEG of a molecular weight other than 5000 can be determined using routine experimentation, for example, using the procedures outlined in Example 1. In general, PEG/PLL grafts of various ratios are synthesized, for example, by varying the relative stoichiometric amounts of each component used in a suitable coupling reaction, and their relative efficacy in preventing a model binding interaction can then be determined. One method for doing this involves determine the extent of cell spreading on an anionic polystyrene surface, either uncoated or coated with the polymers.
The dendrimer is covalently grafted to one end of a PEG block. The dendrimer is a lysine dendrimer which preferably contains between 16 and 128 reactive amine groups, which correlates to a dendrimer of between generation 4 and generation 7. The molecular weight of the PEG is between 500 and 2,000,000, preferably between 5,000 and 100,000.
The multi-layer polymeric material is formed by the ionic interactions of a polycation and a polyanion. There are preferably greater than five alternating layers, more preferably more than ten alternating layers, and most preferably, greater than fifteen alternating layers of the polycationic and polyanionic materials. In a preferred embodiment, the topmost and/or bottommost layers are prepared from materials which include a polycationic tissue binding domain and a nonionic non-tissue binding domain, such as PEG/PLL copolymers.
The polymer is applied in a fluid phase to the tissues or cells to be protected, whereupon the tissue binding domains adsorb the polymeric material to the tissue. The fluid phase can be applied to isolated tissue or to tissue during surgery or by means of a catheter or other less invasive device.
The PEG/PLL copolymers can be used for inhibiting cell-cell contact and tissue adhesion. The PLL polymer adsorbs to cells or tissue, and the PEG polymer does not adsorb to tissue. When the two-domain polymeric material contacts a tissue surface, the tissue-binding domain(s) binds and immobilizes the attached non-binding domain(s), which then generally extends away from the tissue surface and sterically blocks the attachment of other tissues.
The materials can be applied to isolated tissue or to tissue during surgery or by means of a catheter or other less invasive device. The compositions are useful for blocking adhesion and immune recognition and thus may be useful in the treatment of many diseases and physiological disorders, including the prevention of postoperative adhesions, protecting injured blood vessels from thrombosis and intimal thickening relating to restenosis, and decreasing the extent of metastasis of tumor cells in tissues. The materials can be used, for example, as semipermeable membranes, as adhesives as tissue supports, as plugs, as barriers to prevent the interaction of one cell tissue with another cell or tissue, and as carriers for bioactive species. A wide variety of biological and non-biological surfaces, with different geometries, can be coated with these polymeric materials.